For example, an oxygen sensor for measuring the concentration of oxygen in automotive exhaust gas is conventionally known as a sensor having a sensor element to detect a gas under measurement. There is known a sensor element for use in such an oxygen sensor, which includes a bottomed cylindrical solid electrolyte body, an inner electrode formed on an inner surface of the solid electrolyte body and an outer electrode formed on an outer surface of the solid electrolyte body, as disclosed in Patent Documents 1 and 2.
An inner connection terminal is fitted into a rear end portion of the sensor element and electrically connected to the inner electrode. A sensor output lead is connected to a rear end portion of the inner connection terminal. A rod-shaped ceramic heater is inserted in the sensor element such that the inner connection terminal is attached around the ceramic heater.
Further, an outer connection terminal (ground connection terminal) is fitted onto the rear end portion of the sensor element and electrically connected to the outer electrode. A ground lead is connected to a rear end portion of the outer connection terminal.
As shown in FIG. 14(a), the outer connection terminal P1 generally includes a cylindrical outer fitting portion P4 (having left and right curved wing sections P2 and P3) brought into contact with the sensor element from outside and an elongated extension portion P5 extending from a point midway between the left and right wing sections P2 and P3 on an axially upper end of the outer fitting portion P4.
As the lead is connected to an upper end of the extension portion P5 of the outer connection terminal P1, the extension portion P5 is in the form of protruding toward the side on which both of the wing sections P2 and P3 project (toward the inside) and then extending axially upwardly (toward the upper side in the drawing) so that the extension portion P5 can be offset according to the position of the lead. Further, the outer connection terminal P1 is arranged in such a manner that the extension portion P5 passes through a through hole P7 of a ceramic separator P6 as shown in FIG. 14(b).